Get a Service proxy for the Secret Service.
If such a proxy object already exists, then the same proxy is returned.
If flags contains any flags of which parts of the secret service to ensure are initialized, then those will be initialized
before completing.
This method will return immediately and complete asynchronously.
| flags |
flags for which service functionality to ensure is initialized |
| cancellable |
optional cancellation object |
| callback |
called when the operation completes |
| user_data |
data to be passed to the callback |